TDM voice DOS

Anyone been involved with TDM voice DOS attacks? My thoughts are that if the phone call originates as an IP call somewhere in the wild, then typical abuse security incident notifications may help in the interim. At least potentially identify through customer records or make them move on where they eventually slip up. If the abuse originates as IP what obligations do foreign service providers (friendly?) have to identify and mitigate? How can the community respond to service providers who fail to clean up their customer base? Mike